BULLETIN 889 Cover Crops for High-Desert Farming Systems in Idaho Lauren Hunter, Christi Falen, and Amber Moore Introduction A cover crop is any crop grown to provide living ground cover. It can be planted with the main crop or in rotation with it. Growing cover crops is a best management practice to help minimize soil erosion, prevent nutrient leaching, provide nitrogen (N) for subsequent cash crops, suppress weeds, sequester carbon, increase crop diversity, and provide beneficial insect habitats. In Idaho, cover crops can be planted in spring, summer, or fall and rotated with a variety of crops, including barley, alfalfa, potato, sugar beets, beans, and vegetables. By planting cover crops, Idaho producers benefit from Figure 1. A cover crop mixture of canola, triticale, clover, and vetch the following: helps to scavenge nutrients, increase organic matter, fix N, and control weeds. This multi-species cover crop was planted in • Lower N fertilizer costs Lincoln County, Idaho, following grain harvest. • Higher soil organic matter contents turnip, mustard, and canola). Depending on your • Less wind erosion cropping system, the species can be mixed to achieve • Scavenging and retention of soil nutrients multiple management goals. • Weed or insect control For additional general information on cover crop seeding, refer to “Recommended Cover Crop Seeding • Production of a dual-purpose alternative forage Methods and Tools,” which is listed in the references This guide features optimal cover crops for high-desert section. farming systems in the intermountain West under irrigated or low-moisture conditions. The specific Nitrogen and Organic Matter species and varieties listed in this publication were Cover crop selection should be based on the cropping tested under Idaho growing conditions through system’s needs, such as improving soil conditions or numerous on-farm research trials. The species were managing weeds and pests. Planting a mixture of two selected based on cold hardiness, biomass production, or more cover crops can help add N to the soil, N fixing and scavenging abilities, and forage potential. increase soil organic matter, scavenge nutrients, and For each species, information includes optimal planting control weeds (figure 1). dates, N contribution, biomass production, recommended cover crop mixtures, and estimated cost Nitrogen-accumulating crops (legumes) and for cover crop seed. N-scavenging cover crops (brassicas) can reduce the need for N fertilizer. The availability of N from cover The cover crop species are divided into three groups: crops is dependent on the N content in the cover crop (1) cereal and grass cover crops, (2) N-fixing cover plant tissue, incorporation method, incorporation crops, and (3) brassica cover crops (includes radish, timing, and amount of biomass. For example, incorporation of a thick stand of N-rich hairy vetch can contribute a significant amount of N to the following Winter Hardiness, Tillage Practices, crop, while incorporation of N-poor triticale residues can and Irrigation likely tie up N in the soil. Tools like the Idaho cover crop How producers plan to incorporate or manage residue calculator and publications like Estimating Plant- with their available equipment will determine which Available Nitrogen Release from Cover Crops can help species will work best. Some growers may prefer a growers estimate the N contribution from planted cover cover crop that dies in the winter, which makes residue crops (see references and further readings). easier to manage in the spring before cash crop Legumes do not provide as much organic matter as planting. In contrast, species that survive the winter are grasses or grains. A cover crop mixture that contains a beneficial for producers looking to maximize yield, combination of legumes and small grains or grasses resulting in higher contributions of N and organic contributes N and organic matter (figure 2). If growing matter from additional spring growth. Dual-purpose dual-purpose alternative forage is a goal, producers cover crop mixtures should include species that should plant species with good forage potential that are produce both fall and spring forage. Cover crops that safe to graze at a higher seeding rate (figure 3). Dual- winter-kill are advisable for producers who are new to purpose cover crops allow producers to gain an cover crops. economic advantage by grazing the crop before using Common methods used to terminate cover crops in the its residue for soil management. spring include tillage, herbicide, winter-kill, mowing, and roller/crimper. Moldboard plows, rotary tillers, chisel or disking plows, and spaders are examples of tillage tools. Producers who do not want to incorporate cover crops or employ minimum tillage can utilize no-till, strip-till, or mulch-till equipment to plant succeeding crops into existing residue. This practice is beneficial for controlling weeds and minimizing disturbance to the soil. However, under Idaho’s low-moisture environment, not incorporating cover crop residue will slow the release of N. Producers can plant cover crops by broadcast seeding with or without light incorporation of seed. Good seed- to-soil contact and sufficient irrigation during germination will ensure a good stand. Cereal producers have the option to interseed cover crops into existing Figure 2. A cover crop mixture that contains legumes and a winter cereal stubble in the fall or disk the field prior to cereal contributes both N and organic matter to the soil. At left is planting cover crops. Cover crops interseeded into a hairy vetch and triticale mix; at right is an Austrian winter pea cereal stubble can be grazed in the fall for a dual- and triticale mix, Kimberly, Idaho. purpose forage and cover crop mix. Cereal and Grass Cover Crops Cereal grains and grasses are successful cover crops because they contribute organic matter to the soil, reduce seed costs, are widely available, can be planted with existing equipment, germinate quickly, require minimal water, and increase residue yields when planted with a legume. In Idaho, cereal and grass cover crops are a good option to plant after a fall harvest and leave for winter coverage. The large amount of residue protects the soil surface from wind erosion, helps hold soil nutrients, and conserves soil moisture. Grains and grasses can be used as N catch crops, scavenging residual N from fall-applied fertilizer or Figure 3. A higher seeding rate of canola, triticale, clover, and manure/compost. This use of cereals and grasses will vetch makes this dual-purpose cover crop mix ideal for forage, help minimize N loss and conserve residual N for the Minidoka County, Idaho. following growing season. 2 For forage use, cereal cover crops can be planted in Sorghum Sudangrass the spring, summer, or fall and used for fall and spring grazing. A residual 3 to 4 inches should be left Sorghums and sorghum Sudangrasses are warm- for winter coverage and spring regrowth. The species season annuals commonly grown for forage (figure and varieties listed here are selected based on cold 5). Special Effort, Enorma, HayKing, Forage King, hardiness, forage quality, yield potential, and Cadan, and Nutri-Plus sorghum Sudangrasses have all flexibility in a cover crop mix. performed well under Idaho growing conditions. Their fast growth and large biomass production are Even though rye grows well in Idaho, it is not beneficial for suppressing weeds and adding organic included in this publication due to producer concerns matter to the soil. with grain crop contamination. Following grain harvest, volunteer grain stubble can be a part of your Sudangrass can be grown on a variety of soil types, planted cover crop mix. survive in poorer soil, improve worn-out soils, and penetrate compacted soil. It is drought resistant and Pearl Millet can scavenge nutrients due to its many secondary roots. When grazing livestock on Sudangrass, Pearl millet, a warm-season annual grass, provides producers need to test plant tissue to avoid the risks beneficial ground cover and organic matter (figure 4). of high concentrations of nitrates and prussic acid. It is most-widely grown in the southern U.S. as a high- After Sudangrass dies in the fall, the prussic acid nutritive-value emergency forage. It is a tall, erect dissipates, but the nitrates do not. grass that produces several stems from one plant. It has an extensive root system, making it very drought Biomass production: High dry matter yields tolerant as well as a good nutrient scavenger. It does Cold hardiness: Dies at the first frost. The best time to not yield as much as sorghum Sudangrass but is safer grow Sudangrass in Idaho is typically from June for grazing during the growing season because it through September or early October. doesn’t have any prussic acid. Pearl millet is considered a low-input crop; however, it does not Planting dates: Summer, early fall tolerate waterlogged soils. Mixtures: Best planted alone in order to obtain maximum amounts of organic matter for soil Biomass production: Medium dry matter yields incorporation and good weed control. It can be mixed Cold hardiness: Dies at the first frost. The best time to with other species at low seeding rates. Alternate-row grow pearl millet in Idaho is typically from June through planting is an option to keep Sudangrass from September or early October. shading out other planted species. Planting dates: Summer, early fall Seed cost: Medium Mixtures: Grows well with peas and other legumes. Seed cost: Medium Figure 4. A mid-June planting of pearl millet in August (left) and a Figure 5. High-yielding, June-planted sorghum Sudangrass after mid-August planting of pearl millet in October with some frost one month’s growth, Kimberly, Idaho. kill, Kimberly, Idaho. 3 Triticale Winter Wheat Triticale is an annual cereal crop that produces a large Winter wheat is an annual cereal forage that can grow amount of biomass in a relatively short period of time.